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From:Zhangzhigang Date:April 23 2012 3:18am
Subject:Re: Why does the limit use the early row lookup.
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Why does not the mysql developer team to do this optimization?

--- 12年4月20日,周五, Reindl Harald <h.reindl@stripped> 写道:

> 发件人: Reindl Harald <h.reindl@stripped>
> 主题: Re: Why does the limit use the early row lookup.
> 收件人: mysql@stripped
> 日期: 2012年4月20日,周五,下午3:50
> 
> 
> Am 20.04.2012 04:29, schrieb 张志刚:
> > My point is that the limit can use late row lookup:
> lookup rows after
> > checking indexes to optimize the select speed.
> > 
> > But the mysql optimizer do it with the early row
> lookup: lookup all rows
> > before checking indexes when the one fetch column is
> not in the indexes.
> > 
> > Tell me why?
> 
> because the mysql optimizer until now is really
> bad in many situations - order by rand() makes a
> temporary table wil ALL data as example even with limit
> 
> select * from table order by rand() limit 10;
> reads and writes the whole table to disk
> have fun with large tables :-)
> 
> 
Thread
Why does the limit use the early row lookup.张志刚20 Apr
  • Re: Why does the limit use the early row lookup.Reindl Harald20 Apr
    • RE: Why does the limit use the early row lookup.Rick James20 Apr
      • Re: Why does the limit use the early row lookup.Reindl Harald20 Apr
    • Re: Why does the limit use the early row lookup.Zhangzhigang23 Apr
      • Re: Why does the limit use the early row lookup.shawn green23 Apr
        • RE: Why does the limit use the early row lookup.Rick James23 Apr
  • RE: Why does the limit use the early row lookup.Rick James23 Apr
    • RE: Why does the limit use the early row lookup.Zhangzhigang24 Apr
      • RE: Why does the limit use the early row lookup.Rick James24 Apr
Re: Why does the limit use the early row lookup.Jan Steinman25 Apr